[crac] RFR: 8371337: [CRaC] Fastdebug build fails when calling OperatingSystemMxBean.getProcessCpuLoad after restore

[Radim Vansa]

A JVM that executed OperatingSystemImpl.getProcessCpuLoad()  before checkpoint can fail with assertion failure after restore with:

java: /home/rvansa/work/zulu/src/jdk.management/linux/native/libmanagement_ext/UnixOperatingSystem.c:291: get_cpuload_internal: Assertion `pticks->usedKernel >= tmp.usedKernel' failed.

This is an assertion failure, therefore failing only in debug builds, and providing probably a non-sense value in release builds. We should remove the assertion and return a negative value (documented as value for ‘unavailable’) if this is detected.

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Commit messages:
 - 8371337: [CRaC] Fastdebug build fails when calling OperatingSystemMxBean.getProcessCpuLoad after restore

Changes: https://git.openjdk.org/crac/pull/274/files
  Webrev: https://webrevs.openjdk.org/?repo=crac&pr=274&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8371337
  Stats: 65 lines in 2 files changed: 62 ins; 3 del; 0 mod
  Patch: https://git.openjdk.org/crac/pull/274.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/274/head:pull/274

PR: https://git.openjdk.org/crac/pull/274